The invention relates to a method for detecting flaws and comparable, radiation-reflecting defects in the walls of hollow glass items.
Known from document CH 652826 A5 is a device for optically detecting flaws in transparent bodies, in which a number of radiation sources is allocated to a glass body that rotates around its longitudinal axis during an inspection. Located opposite the radiation sources are detectors accommodated in detector blocks as the radiation receivers. In order to counteract the reception of interference radiation, subsystems are formed that each consist of radiators and radiation receivers, wherein these subsystems are activated one after the other, and not simultaneously. These subsystems enable a suppression of interference radiation from the environment. However, a high level of experience is required for expediently creating the subsystems tailored to the individual case, here to the glass body to be inspected.
Interference radiation detracts from the strength of the evaluated received radiation, and can arise in a variety of ways from the ambient conditions, e.g., in the form of extraneous light sources, but can also stem from the shape of the hollow glass item to be inspected, e.g., reflections on rotationally symmetrical structural elements that are independent of a potential rotation of the hollow glass item, or the respective camera angle at which these reflections are recorded by a fixed radiation receiver. As a consequence, the received radiation is always composed of useful and interference signals.
A plurality of potential solutions has become known for separating useful and interference signals in conjunction with the flaw inspection of hollow glass items. EP 0 692 710 B1 describes a method and device for image processing to check for light-reflecting defects, wherein a hollow glass item rotates around its longitudinal axis, and wherein sequential images offset relative to each other by a rotational angle are generated by an incident light beam as a function of rotation. By comparing at least two sequential images, constantly reflected scatter reflections are differentiated from variable useful reflections pointing to local defects of the hollow glass item during the evaluation. As a consequence, the evaluation of reflections here depends on the sequence of the first images.
The differentiation between useful and interference signals is of significant importance during the automated flaw detection in hollow glass items. A faulty interpretation of an interference signal as a useful signal results in an item being discarded unnecessarily as unusable. As a consequence, there exists a strong interest in effectively detecting and masking out any interference signals, so that the respective item can be inspected based exclusively on useful signals.